Chlorinated solvents and petroleum hydrocarbons have long been used by industry, including the military, dry cleaners, and other businesses. Their use has resulted in releases into the environment which have contaminated soils and groundwater, which generate vapors of these contaminants that migrate through the vadose zone and through utility trenches and sewers and accumulate under buildings and migrate or threaten to migrate into the indoor air of these buildings, and also intrude directly into buildings via sewer vapor leaks, thereby endangering the health of their inhabitants.
Chlorinated solvents have persisted in the environment for many decades and the threat of the impact to human health from their vapors is the leading concern of their contamination of the environment. These chlorinated solvents and their degradation products are toxic to human health and many are also carcinogenic. While petroleum hydrocarbons do not exhibit the same persistence as chlorinated solvents in the environment, they too are toxic and some are carcinogenic.
While there are known remediation technologies and processes applied to soils and groundwater contaminated by chlorinated solvents and petroleum hydrocarbons, there are no remedial processes currently available for the vapors generated by such contamination which have accumulated under buildings and threaten the health of their inhabitants. The presence of such chlorinated vapors in the sub-slab of buildings is conventionally addressed via mitigation, through their venting to the atmosphere by depressurizing the sub-slab space rather than by elimination through remediation. The same is true for petroleum compounds.
The sub-slab vapor mitigation processes and systems presently used are not reliable, due to inherent concerns with the principle of their application and appropriateness, as they don't actually remediate the contamination, but rather transfer it from one location to another. Serious concerns have also been documented with regards to their design, installation, operation and maintenance, and measured effectiveness. As a result, the installation of a vapor mitigation system cannot assure the risk to the health of the building's inhabitants will be reduced to acceptable levels.
Mitigation, furthermore, even if effective, would require long term operation, maintenance and monitoring of the sub-slab vapors and indoor air, and the placement of a restrictive covenant on the deed of the property regarding the need to have, at all times, a vapor mitigation system operating at that building.